Device for changing the control timing of gas exchange valves of an internal combustion engine, particularly a rotary piston adjustment device for rotation angle adjustment of a camshaft relative to crankshaft

ABSTRACT

A device for changing the control times of gas exchange valves of an internal combustion engine, particularly a rotary piston adjusting device for rotation angle adjustment of a camshaft relative to a crankshaft, which device is fastened by a central fastening screw to a camshaft mounted in the cylinder head of the internal combustion engine. The device includes a stator, in driving connection with the crankshaft and having two side covers, and of a rotor connected to rotate with the camshaft, with at least two hydraulic working spaces being formed in the stator by at least two radial boundary walls. The chambers are divided by at least two radial vanes on the rotor, respectively, into two hydraulic pressure chambers which work in opposition to one another. The stator and the one side cover of the device are formed as an integral stator unit, and the rotor and the other side cover are formed as an integral rotor unit. These are fixed together axially and radially and to the camshaft by the central fastening screw and by additional positive locking elements on the drive-side end of the camshaft or on the head of the fastening screw.

BACKGROUND

[0001] The invention relates to a device for changing the control times of gas exchange valves of an internal combustion engine, and it can be implemented with particular advantage in a rotary piston adjustment device for rotation angle adjustment of a camshaft relative to a crankshaft.

[0002] One such device which is already known is shown in EP 0 799 976 A1. This device is fastened by means of a central fastening screw on the drive-side end of a camshaft mounted in the cylinder head of the internal combustion engine, and in principle is formed as a hydraulic actuator, which essentially includes a stator with two axial side covers, in driving connection with the crankshaft of the internal combustion engine, and a rotor which is connected to rotate with the camshaft of the internal combustion engine. The stator of the device includes a hollow cylindrical circumferential wall, to the outside of which a chain sprocket is fastened, and on the inside of which four boundary walls are arranged directed toward the longitudinal central axis of the device and uniformly distributed circumferentially, with four hydraulic working spaces formed between them. The rotor of the device correspondingly includes a hub with four uniformly circumferentially distributed radial vanes which extend into the working spaces of the stator and divide each of the chambers, respectively, into two hydraulic pressure chambers acting in opposition to one another. These pressure chambers can be acted on selectively or simultaneously with a hydraulic pressure medium via a hydraulic control valve and various pressure medium channels so that a relative rotation or fixing of the rotor relative to the stator takes place, and thereby of the camshaft relative to the crankshaft.

[0003] This device, sometimes referred to as a pivoting vane adjuster, has however been found to be disadvantageous, as have the devices known as vane cell adjusters in which the rotor is separable into a hub and individual, mostly spring-supported vanes, in that it is produced in a multi-piece construction and is thus composed of a relatively large number of individual parts. Hence for each individual part the interface to the respective communicating parts must be precisely defined, in order to reduce to a minimum the accumulation of tolerances associated with manufacturing and, connected thereto, the large tolerance width for functional play and leakage gaps within the device. Such measures however involve for the most part a high failure risk, and assume expensive logistics and stockkeeping, and also precise manufacturing of individual parts. A high assembly cost, and the risk of malfunctions of the device due to the failure of individual parts, are furthermore associated with the large number of individual parts, resulting in an overall high cost for such devices. Moreover a further disadvantage of the known device is that the stator and the side cover of the device are connected together by separate cover screws, since radial and axial deformations or component stresses result from the forces introduced by the cover screws and likewise are to be taken into account in the definition of the interfaces with regard the maintenance of axial and radial play, and smallest possible leakage gaps within the device. In the most unfavorable case, these component stresses in the individual parts of the device can become so high that the screw connection of the side cover to the stator fails, resulting in engine damage.

SUMMARY

[0004] The object of the invention is therefore to provide a device for changing the control times of gas exchange valves of an internal combustion engine, particularly a rotary piston adjustment device for rotation angle adjustment of a camshaft relative to a crankshaft, which is composed of a minimum of individual parts and also is distinguished by a low manufacturing and assembly cost, and in which component stresses caused by connecting elements between the individual parts can be avoided.

[0005] According to the invention, the object is attained with a device comprising a stator in driving connection with the crankshaft of the internal combustion engine, having two axial side covers, and a rotor connected to rotate with the camshaft of the internal combustion engine. The stator is formed from a hollow cylindrical circumferential wall and at least two boundary walls directed radially to the longitudinal central axis of the device. At least two working spaces are formed between the at least two boundary walls. The rotor comprises a hub with at least two radial vanes which extend into the working spaces of the stator and divide these into respectively at least two hydraulic pressure chambers acting in opposition to one another. Upon selectively or simultaneously acting on the pressure chambers with a hydraulic pressure medium, a relative rotation or fixing of the rotor takes place relative to the stator and thereby of the camshaft relative to the crankshaft. The stator and the one axial side cover of the device are formed as an integral stator unit, and also the rotor and the other axial side cover of the device are formed as an integral rotor unit, which are axially and radially fixed together and to the camshaft solely by the central fastening screw of the device and by additional positive locking elements on the drive-side end of the camshaft or on the head of the fastening screw.

[0006] Such an assembly of the device is carried out by integral metal construction, and thus limits the number of essential individual parts of the device to two construction units and the central fastening screw. However, since in such an integral construction hollow corners arise on the stator unit and on the rotor unit due to the method of construction and could be produced only at great cost by machining, both the stator unit and the rotor unit are, according to an expedient development of the device in accordance with the invention, produced as sintered steel press-molded parts, without machining. The chain sprocket or belt rim for the drive connection to the crankshaft of the internal combustion engine is likewise formed on the circumferential wall of the stator unit. For devices designed for light construction, it is on the other hand advantageous to produce the stator unit and the rotor unit, or selectively also only one of the two construction units, without machining, as aluminum or magnesium diecast parts or as plastic injection molded parts, and to fasten a separate chain sprocket or belt rim of steel to the stator unit. Interference between the corners of the vanes of the rotor unit and the production process-determined radii of the hollow corners of the stator unit can furthermore be avoided in a simple manner by the formation of corresponding bevels on the axial and radial edges of the vanes.

[0007] The positive locking elements required in the fixing of both construction units of the device by the central fastening screw are furthermore, in a specific embodiment of the device in accordance with the invention, preferably arranged on the drive-side end of the camshaft and formed such that a stub of reduced diameter is formed on the front side of the camshaft and a stepped shoulder is machined into the front side of the camshaft. The stepped shoulder preferably has a greater diameter than the stub at the front side of the camshaft and has a width which is slightly greater than the thickness of the side cover of the stator unit. The stub at the front side of the camshaft on the contrary again has a greater diameter than the axial bore in the hub of the rotor unit, and is formed with an optional length sufficient for the radial fixing of the rotor unit. The threaded bore required for the central fastening screw is machined through this stub into the drive-side end of the camshaft, and can likewise be used in a known manner, by means of an inserted oil separation sleeve, for supply and discharge of pressure medium to and from the pressure chambers of the device. However it is also possible, in an exactly reverse manner, to fasten the device to a front side of the camshaft formed without a stub and stepped shoulder, and to fix it axially and radially to the camshaft by identical or similarly formed positive locking elements on the head of the fastening screw.

[0008] Corresponding to the described positive locking elements on the driveside end of the camshaft, the device according to the invention is furthermore characterized by the feature that the rotor unit is radially positively fixed to the stub of the camshaft with the axial bore of its hub on the camshaft side, widened to the diameter of the stub on the end of the camshaft, while it likewise abuts with the camshaft-side side surface of its hub on the front side of the camshaft, and is axially fixed to the camshaft by the screwing-on moment of the central fastening screw. The screwing-on moment of the central tightening screw is here to be adjusted so that the rotor unit is likewise also fixed to the camshaft, to rotate with it in the circumferential direction, and the torque acting on the rotor unit from the crankshaft of the internal combustion engine via the stator unit can be reliably transmitted to the camshaft. To ensure such a fixation of the rotor unit to the camshaft in the circumferential direction, it can therefore be advantageous to form the stub on the camshaft and the widened axial bore in the hub of the rotor unit conically, in order to increase the locking between the rotor unit and the camshaft, or to provide additional key toothing or the like, in order to secure the connection between the rotor unit and the camshaft by additional positive locking.

[0009] In contrast to this, the stator unit, as a further feature of the device according to the invention, only abuts on the hub of the rotor unit with the correspondingly concavely formed inner front side of its radial boundary walls, and is thereby rotatably mounted on the rotor unit and also, through this, radially positively fixed to the camshaft. The axial fixation of the stator unit to the camshaft takes place, on the contrary, such that the side cover of the stator unit directed toward the camshaft abuts with its inner side on the side surface toward the camshaft of the hub of the rotor unit and hence is fixed in the axial direction remote from the camshaft. Furthermore the side cover of the stator unit has an axial opening which is formed with a slightly greater diameter than the stepped shoulder on the camshaft, and with which the side cover encloses the shoulder on the camshaft such that, due to the vertical annular surface of the stub on the camshaft, the stator unit is also no longer movable in the axial direction toward the camshaft. The stator unit is consequently arranged with its side cover between the camshaft-side side surface of the hub of the rotor unit and the vertical annular surface of the stepped shoulder in the front side of the camshaft, and is thus also positively fixed in position axially relative to the camshaft. The slightly wider construction of the stepped shoulder on the camshaft compared with the thickness of the side cover of the stator unit here ensures that the stator unit is not clamped between the rotor unit and the camshaft and is freely movable at all times in the circumferential direction on the rotor unit. Likewise the axial opening in the side cover of the stator unit, which has a larger diameter than the stepped shoulder on the camshaft, has the background that no further external bearing region for the stator unit arises, over and above the internal mounting of the stator unit on the rotor unit. However, instead of the internal mounting of the stator unit on the rotor unit, an external mounting is also possible.

[0010] With respect to the remaining connection between the stator unit and the rotor unit, in a further embodiment of the device according to the invention, it is furthermore possible to form the circumferential wall of the stator unit, on its side remote from the camshaft, with an edge portion which is axially lengthened in comparison with the width of its radial boundary walls, and which with its inner surface surrounds the circumferential surface of the side cover of the rotor unit and with its front face is situated opposite to an annular land that is also arranged on the circumferential surface of the side cover of the rotor unit. With this construction, the rotor unit and the stator unit of the device are advantageously mutually closed, with the extended edge portion of the circumferential wall of the stator unit again abutting on the circumferential surface of the side cover of the rotor unit, to avoid an external bearing region, likewise abutting just as little directly on the circumferential surface of the side cover of the rotor unit as on its front surface, in order to avoid axial over fixing between the rotor unit and the stator unit at the annular land. In a simplified variant, it is also possible in this respect to completely omit the annular land on the circumferential surface of the side cover of the rotor unit, and to form the circumferential wall of the stator unit with a lengthened edge portion extending over the whole width of the circumferential surface of the side cover of the rotor unit.

[0011] As a last feature of the device according to the invention, it is also possible to arrange an additional sealing element between the circumferential surface of the side cover of the rotor unit and the inner surface of the lengthened edge portion of the circumferential wall of the stator unit, in order as far as possible to avoid external pressure medium leaks on the device. A steel sealing ring inserted in an annular groove in the circumferential surface of the side cover of the rotor unit has been found to be particularly advantageous here. Alternatively, an O-ring seal or another suitable shaped seal can be used in place of it. Furthermore, additional sealing elements are conceivable in the axial and/or radial direction on the vanes of the rotor unit, such as, for example, simple or angled sealing strips, in order to also prevent internal leaks between the pressure chambers of the device as much as possible.

[0012] The device according to the invention for changing the control times of gas exchange valves of an internal combustion engine, in particular a rotary piston adjusting device for rotation angle adjustment of a camshaft relative to a crankshaft thus has the advantage, in contrast to the devices known from the state of the art, that by the making the side covers of the device as part of the stator and the rotor, the device is now produced in an integral construction and the number of individual parts of the device is substantially reduced to a stator unit, a rotor unit, and a central fastening screw. The expensive defining of the interfaces between the respective interfacing individual parts in the multi-piece construction is thereby omitted, so that the tolerance widths with functional play within the device are also reduced and the cost for logistics, stock-keeping, and the manufacture of individual parts are reduced to a minimum. Furthermore the reduction of the individual parts of the device has the further consequence that the assembly cost for the device and also the risk of malfunctions of the device due to the failure of individual parts is minimized and the device can thus be produced more cost-favorably. Also, since cover screws are no longer necessary for connecting the side cover to the stator in the device according to the invention, there is also a weight advantage in comparison with the known devices, and the deformations or component stresses which resulted from the screw force of these cover screws can no longer occur.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The invention is explained in further detail below with reference to a preferred embodiment, which is schematically shown in the accompanying drawings.

[0014]FIG. 1 is a longitudinal section view taken along line 1-1 in FIG. 2 through a device according to the invention.

[0015]FIG. 2 is a cross-sectional view taken along line 2-2 in FIG. 1 of the device according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0016] A device 1 for changing the control times of gas exchange valves of an internal combustion machine, formed as a rotary piston adjustment device for rotation angle adjustment of a camshaft 5 relative to a crankshaft (not shown) of an internal combustion engine, is shown in FIGS. 1 and 2. This device 1 is fastened by a central fastening screw 2 to the drive-side end 3 of a camshaft 5 mounted in the cylinder head 4 of the internal combustion engine, and is in principle formed as a hydraulic actuator, which is controlled based upon various parameters of the internal combustion engine by a hydraulic valve, not shown in detail in FIG. 1. Moreover, it can be seen in FIGS. 1 and 2 that the device 1 is substantially formed from a stator 6 which is in driving connection with the crankshaft of the internal combustion engine and which has two axial side covers 7, 8, and a rotor 9 connected to rotate with the camshaft 5 of the internal combustion engine. The stator 6 of the device 1 comprises a hollow cylindrical circumferential wall 10 and five boundary walls 11 directed toward the longitudinal central axis of the device 1 and having five working spaces 12 formed between them and uniformly distributed circumferentially. The rotor 9 of the device 1, particularly clearly recognizable in FIG. 2, correspondingly comprises a hub 13 with five uniformly circumferentially distributed vanes 14 which extend into the working spaces 12 of the stator 6 and divide these each, respectively, into two hydraulic pressure chambers 15, 16 which act in opposition to one another. The pressure chambers 15, 16 can be selectively or simultaneously acted on by a hydraulic medium via the pressure medium channels, such as those shown in the drawings, with the effect that, during the operation of the internal combustion engine, a relative rotation or fixation of the rotor 9 with respect to the stator 6, and therewith a rotation angle adjustment or hydraulic clamping of the cam shaft with respect to the crankshaft, takes place.

[0017] It can furthermore be seen, particularly from FIG. 1, that in the device 1, in order to minimize the number of individual parts, according to the invention, the stator 6 and the axial side cover 7 are formed as an integral stator unit 17, and the rotor 9 and the other axial side cover 8 are formed as an integral rotor unit 18, which are fixed together and to the camshaft 5, axially and radially solely by the central fastening screw 2 of the device 1 and by additional positively locking elements on the drive-side end 3 of the camshaft 5. Both the stator unit 17 and also the rotor unit 18 of the device 1 are here produced without machining, and the chain sprocket, not shown in detail in the drawing, for the drive connection to the crankshaft of the internal combustion engine, likewise is formed on the circumferential wall 10 of the stator unit 17.

[0018] The positive locking elements on the drive-side end 3 of the camshaft 5 for fixing the stator unit 17 and the rotor unit 18 together and to the camshaft are also shown in FIG. 1 and are specifically formed by a stub 20 formed at the front side 19 of the camshaft 5 and by a stepped shoulder 21 machined into the front side 19 of the camshaft 5. The rotor unit 18 of the device 1 correspondingly has in its hub 13 an axial bore 22 which is widened out on the camshaft side to the diameter of the stub 20 on the camshaft 5, and it is pushed onto the stub 20 and can thus be radially positively fixed to the camshaft 5. The rotor unit 18 is pushed onto the stub 20 until it abuts with the side surface 23 of its hub 13 on the front 19 of the camshaft 5 and can be fixed in the axial direction and likewise in the circumferential direction, on the camshaft 5, by the screwing-on moment of the central fastening screw 2.

[0019] The stator unit 17, on the other hand, as can clearly be seen in FIG. 2, is rotatably mounted on the rotor unit 18, with the radial front sides 24 of its boundary walls 11 abutting on the outside surface 25 of the hub 13 of the rotor unit 18, and is thus already positively fixed to the camshaft 5 in the radial direction. The fixation of the stator unit 17 in the axial direction takes place such that its side cover 8 abuts on the camshaft-side side surface 23 of the hub 13 of the rotor unit 18 and has an axial opening 26 formed slightly larger in diameter than the stepped shoulder 21 on the camshaft 5 and with which the side cover 8 encloses the shoulder 21 on the camshaft 5. The stator unit 17 is thereby arranged with its side cover 8 between the camshaft-side side surface 23 of the hub 13 of the rotor unit 18 and the vertical annular surface 27 of the stepped shoulder 21 in the front side 19 of the camshaft 5, and is thus also positively axially fixed with respect to the camshaft 5.

[0020] Finally, it can also be seen from FIG. 1 that the circumferential wall 10 of the stator unit 17, for connection to the rotor unit 18, has on its side remote from the camshaft an edge portion 28, axially lengthened in comparison with the width of its radial boundary walls, enclosing with its inner surface 29 the circumferential surface 30 of the side cover 7 of the rotor unit 18, and situated with its front face 31 opposite to an annular land 32 additionally arranged on the circumferential surface 30 of the side cover 7 of the rotor init 18. To prevent external pressure medium leaks, an additional sealing element 33 is arranged between the circumferential surface 30 of the side cover 7 of the rotor unit 18 and the inner surface 29 of the edge portion 28 of the circumferential wall 10 of the stator unit, and is indicated in FIG. 1 as a steel sealing ring inserted in an annular groove 34 in the circumferential surface 30 of the side cover 7 of the rotor unit 18.

[0021] Reference Numerals 1 device 18 rotor unit 2 fastening screw 19 front side of 5 3 drive-side end 20 stub on 19 4 cylinder head 21 shoulder in 19 5 camshaft 22 axial bore in 13 6 stator 23 side face of 13 7 side cover 24 radial front side of 11 8 side cover 25 outer surface of 13 9 rotor 26 axial opening in 8 10 circumferential wall 27 annular surface of 21 11 boundary walls 28 edge portion of 10 12 working spaces 29 inner face of 28 13 hub 30 circumferential surface of 7 14 vane 31 front face of 28 15 pressure chamber 32 annular land on 30 16 pressure chamber 33 sealing element 17 stator unit 34 annular groove in 30 

1. Device for changing the control times of gas exchange valves of an internal combustion engine of a rotary piston adjustment type for rotation angle adjustment of a camshaft relative to a crankshaft, comprising: a central fastening screw to fasten the device to a drive-side end of a camshaft mounted in a cylinder head of the internal combustion engine, a stator in driving connection with the crankshaft of the internal combustion engine, having two axial side covers and of a rotor connected to rotate with the camshaft of the internal combustion engine, the stator including a hollow cylindrical circumferential wall and at least two boundary walls directed radially toward a longitudinal central axis of the device, at least two working spaces being formed between the at least two hydraulic boundary walls, the rotor including a hub with at least two radial vanes which extend into the working spaces of the stator and divide the working spaces, respectively, into at least two hydraulic pressure chambers acting in opposition to one another, upon selectively or simultaneously acting on the pressure chambers with a hydraulic pressure medium, a relative rotation or fixing of the rotor takes place relative to the stator and thereby of the camshaft relative to the crankshaft, the stator and the one axial side cover of the device are formed as an integral stator unit, and the rotor and the other axial side cover of the device are formed as an integral rotor unit which are axially and radially fixed together and to the camshaft solely by the central fastening screw and positive locking elements on a drive-side end of the camshaft or on a head of the fastening screw (2).
 2. The device according to claim 1, wherein the stator unit and the rotor unit are produced as one of sintered steel compression molded parts, aluminum or magnesium diecast parts or as plastic injection molded parts.
 3. Apparatus according to claim 1, wherein the positive locking elements are arranged on the drive-side end of the camshaft and comprise a reduced-diameter stub and a stepped shoulder machined in a front side of the camshaft.
 4. Device according to claim 3, wherein the rotor unit is positively fixed radially to the stub of the camshaft, by a camshaft-side axial bore in the hub having a widened portion which fits on the stub on the camshaft, and the rotor is axially fixed to the camshaft by a screwing-on moment of the central fastening screw, with a camshaft-side side face of the hub abutting on a front of the camshaft.
 5. Device according to claim 3, wherein the stator unit is rotatably mounted on the rotor unit with radial front sides of the boundary walls abutting on an outside surface of the hub of the rotor unit, and is also thereby positively fixed radially to the camshaft (5), and wherein the side cover of the stator unit is arranged with an axial opening enclosing a stepped shoulder on the camshaft between a vertical annular surface and the camshaft-side side surface of the hub of the rotor unit, and the stator unit is thus also positively fixed axially with respect to the camshaft.
 6. Device according to claim 1, wherein the circumferential wall of the stator unit has, on a side remote from the camshaft, an edge portion, axially lengthened in comparison with a width of the radial boundary walls, which encloses with an inner surface thereof a circumferential surface of the side cover of the rotor unit and is situated with an end face of the edge portion opposite to an annular land arranged on the circumferential surface of the side cover of the rotor unit.
 7. Device according to claim 6, wherein an additional sealing element is inserted between the circumferential surface of the side cover of the rotor unit and the inner surface of the edge portion of the circumferential wall of the stator unit.
 8. The device of claim 7, wherein the sealing element is one of a steel sealing ring or an 0-ring seal inserted into an annular groove in the circumferential surface of the side cover of the rotor unit. 